Electrochemical machining apparatus having electrolyte pressure responsive load compensating means

ABSTRACT

This application discloses an electrochemical machining or electrolytic demetallizing apparatus adapted to drive a shaping cathode toward and into a conductive metal workpiece, with a gap that is maintained between the cathode and workpiece being filled by pressurized, rapidly flowing electrolyte through which electric current flows between the cathode and workpiece. The apparatus contains drive means for producing relative movement of the cathode and workpiece at a constant rate along a path that determines the shaping of the workpiece. Also, a hydraulic load compensating means urges the cathode forward into the workpiece to at least partially counteract the tendency of the electrolyte pressure to produce relative retracting movement between the cathode and the workpiece. The load compensating means is directly responsive to a change of electrolyte pressure between cathode and workpiece, so that the load-compensating force is relieved upon a sudden decrease in the electrolyte pressure such as may be occasioned when the electrode breaks through the workpiece upon completion of the shaping step. The load compensating means may be separate from the cathode mounting means, or it may include a sealed pressure chamber that encloses the cathode, the cathode-mounting means, and the workpiece, with an insulating spacer in sealing contact with both the chamber wall and the workpiece. In the latter case, passages are provided for draining off electrolyte that may leak through the seal between the insulating spacer and the workpiece.

United States Patent [72] Inventor Lynn A. Wllliams Winnetka, Ill.

[21] Appl. No. 848,962

[22] Filed Aug. 11, 1969 [45] Patented Oct. 26, 1971 [73] Assignee Anoeut Engineering Company Continuation-impart of application Ser. No. 680,811, Nov. 6, 1967, now abandoned and a continuation-in-part of 762,077, Sept. 24, 1968.

[54] ELECTROCHEMICAL MACHINING APPARATUS HAVINGELECTROLYTE PRESSURE RESPONSIVE LOAD COMPENSATING MEANS 19 Claims, 9 Drawing Figs.

[52] US. Cl 204/224,

[51] Int. Cl. 823p 1/02,

823p 1/12 [50] Field of Search 204/224, 225, 143 M [56] References Cited UNITED STATES PATENTS 3,399,125 8/1968 Mikoshiba et a1. 204/224 X 3,409,535 11/1968 Ross et al 204/225 X 3,475,303 10/1969 Sadler et a1 204/143 M FOREIGN PATENTS 1,045,634 10/1966 Great Britain 204/224 Primary Examiner-John l-l. Mack Assistant Examiner-D. R. Valentine Attorney-Dressler, Goldsmith, Clement & Gordon ABSTRACT: This application discloses an electrochemical machining or electrolytic demetallizing apparatus adapted to drive a shaping cathode toward and into a conductive metal workpiece, with a gap that is maintained between the cathode and workpiece being filled by pressurized, rapidly flowing electrolyte through which electric current flows between the cathode and workpiece. The apparatus contains drive means for producing relative movement of the cathode and workpiece at a constant rate along a path that determines the shaping of the workpiece. Also, a hydraulic load compensating means urges the cathode forward into the workpiece to at least partially counteract the tendency of the electrolyte pressure to produce relative retracting movement between the cathode and the workpiece. The load compensating means is directly responsive to a change of electrolyte pressure between cathode and workpiece, so that the load-compensating force is relieved upon a sudden decrease in the electrolyte pressure such as may be occasioned when the electrode breaks through the workpiece upon completion of the shaping step. The load compensating means may be separate from the cathode mounting means, or it may include a sealed pressure chamber that encloses the cathode, the cathode-mounting means, and the workpiece, with an insulating spacer in sealing contact with both the chamber wall and the workpiece. in the latter case, passages are provided for draining off electrolyte that may leak through the seal between the insulating spacer and the workpiece.

PATENTEDHBT 2 3.616.433

SHEET 2 UF 6 PATENTEDUET 26 IQYI SHEET 3 [IF 6 d l \NW MW.

MN mm KQN \N @WN M mm WNW QNN WWW PATENTEDum 26 ml SHEET '4 BF 6 W N60 m3 WNW ELECTROCHEMICAL MACHINING APPARATUS HAVING ELECTROLYTE PRESSURE RESPONSIVE LOAD COMPENSATING MEANS CROSS-REFERENCE TO RELATED APPLICATIONS BACKGROUND OF THE INVENTION Field of the Invention.

Electrochemical machining, or electrolytic demetallizing, is a now well-known process involving the removal of metal from an anodic workpiece by maintaining a stream of electrolyte between the workpiece and a shaping cathode which is not in mechanical contact with the workpiece, while passing direct current therebetween through the stream of liquid electrolyte. See, for example, US. Pat. Nos. 3,058,895 and 3,130,140.

Electrochemical machining can be used to sink cavities and to produce shapes in metal, including hard alloys which are machined conventionally with he utmost difficulty.

Opposing Force from High Electrolyte Pressure The best results are obtained in the electrochemical machining process when the workpiece is spaced only a very short distance from the shaping cathode, and electrolyte flows through the gap between workpiece and cathode at a high velocity and relatively high pressure, frequently 200 p.s.i. or above.

In the use of cathodes of large cross-sectional area, the hydrostatic force tending to push the cathode away from the work becomes quite large. If, for example, the effective crosssectional area of the cathode is, say, 100 sq. in., and if the effective hydrostatic pressure of electrolyte between the cathode and the workpiece is, say, 200 p.s.i., then the total force rises toward 20,000 lbs., the exact value being dependent upon the extent of the Bernoulli effect and the consequent static pressure in the work gap.

The mechanism required to move the cathode toward the workpiece against such a force in a smooth and uniform manner is heavy and expensive. Also, it becomes extremely difficult to move the cathode at a unifonn rate of advance against such high back pressures, although a uniform rate of advance is generally important for the erosion of uniformly shaped cavities.

Need for Prompt Shutoff of Load Compensating Means It is known to provide an additional load compensating means for an electrochemical machining apparatus having a cathode of large cross-sectional area that is subject to strong reaction forces as just described.

While the known load compensating means, such as a hydraulic system arranged to augment the drive system in accordance with the actual electrolyte pressure, successfully assists the drive means in providing a steady advance of the cathode by partially compensating for the hydrostatic force opposing such advance of the cathode, a problem arises at the point where the cathode fully penetrates the workpiece and breaks through the back surface. The electrolyte pressure between cathode and workpiece immediately drops, suddenly reducing the opposing reaction force on the cathode. If the load compensating means is not deactivated immediately when the electrolyte pressure falls, the continued forward force applied by the load-compensating means will cause the cathode to impact with the workpiece, causing damage to both.

Advantages of the Invention This invention provides electrochemical machining apparatus which is particularly suitable for use with shaping cathodes of large cross-sectional area, against which opposing reaction forces of up to 10 tons or more can be developed by the pressurized electrolyte without the above stated undesirable effects taking place.

The apparatus of this invention can be used to erode large cavities in metal workpieces, and upon a sudden drop in electrolyte pressure, caused for example by a breakthrough at the back of the workpiece, the cathode does not surge forward into contact with the workpiece, and thus does not damage the cathode or workpiece.

SUMMARY OF THE INVENTION This application relates to an electrochemical machining apparatus which contains means for mounting a shaping cathode in predetermined position with respect to a conductive metal workpiece to define a gap therebetween, means for flowing electrolyte between the cathode and the workpiece and through said gap under positive pressure, the electrolyte pressure tending to produce relative retraction between the cathode and the workpiece, and means for controlling relative movement between the cathode and the workpiece to maintain a predetermined gap in the presence of the electrolyte pressure, said last-named means including drive means for producing relative movement of the cathode and workpiece along a path that determines the shaping of the workpiece, and load-compensating means for at least partially opposing said tendency to relative retraction between the cathode and the workpiece, said compensating means being directly responsive to electrolyte pressure between the cathode and the workpiece for relieving the load-compensating means upon a sudden decrease in said electrolyte pressure. The loadcompensating means may be separate from the cathodemounting means, or it may include a sealed pressure chamber that encloses the cathode, the cathode-mounting means, and the workpiece, with an insulating spacer in sealing contact with both the chamber wall and the workpiece.

THE DRAWINGS In the drawings:

FIG. 1 is a diagrammatic lengthwise section showing one embodiment of the apparatus of this invention in the operation of eroding a cylindrical hole through a conductive metal workpiece.

FIG. 2 is a diagrammatic lengthwise section showing another embodiment of the apparatus of this invention is the same operation invention. eroding a cylindrical hole through a conductive metal workpiece.

FIG. 3 is a sectional view taken along a vertical plane passing through another embodiment of the apparatus of this invention.

FIG. 4 is a sectional view, taken along line 44 of FIG. 3, of the same apparatus.

FIG. 5 shows a modification of a portion of the apparatus of FIGS. 3 and 4, taken in section along a vertical plane.

FIG. 6 is a sectional view taken along line 6-6 of FIG. 5.

FIG. 7 is a partial sectional view taken along line 7-7 of FIG. 5.

FIG. 8 shows another modification of the apparatus of FIGS. 3 and 4, taken in section along a vertical plane.

FIG. 9 is a sectional view taken along line 9-9 of FIG. 8.

DESCRIPTION OF SPECIFIC EMBODIMENTS Referring to FIG. I, a hollow, cylindrical shaping electrode 2 is carried by a hollow holder 4 to be advanced toward a conductive metal workpiece 6 to form a narrow gap therebetween.

A pressurized liquid electrolyte supply system for maintaining a stream of electrolyte flowing across the gap includes an electrolyte storage container 8, a feed line 9 equipped with a pressure pump P, and a slidable feed bushing 10. The feed bushing 10 serves as a guide cylinder for the electrode holder or cathode-mounting means 4 and is adapted to engage in sprocket 28 for driving a sprocket 29 on sealing relation against the workpiece and provide an annular flow space that surrounds the gap and confines the electrolyte against escape. A return line 12 for the electrolyte leads from the holder 4 to complete the primary electrolyte flow path. This path is shown to lead reversely through the electrode and electrode holder, i.e., from outside the electrode through the work gap between the electrode and the workpiece and then into the interior of the electrode.

The slidable feed bushing may be of any suitable electrically insulating material. it houses the holder 4 and cathode 2 in a relationship to permit electrolyte pressure to cause the bushing to be held in sealed engagement against the workpiece 6.

The feed mechanism for advancing the electrode and electrode holder is designated generally at 14 and includes adapter plates 16, 17, plate 16 being of any suitable electrically insulating material connected in thrust transmitting relation to the rear end of the electrode holder 4. If the electrode cathode assembly is large, there will be a high force against advance of the cathode. The drive system may then be augmented by a load-compensating means to be described below that is separate from electrode holder or cathode-mounting means 4 and is capable of producing a strong additional forward thrust.

Variations in electrolyte pressure at the gap region, whether caused by variation in the supply pressure or by other environmental changes in the electrolyte flow system, impose transient demands upon the drive system that could, in the absence at such a load-compensating means, lead to erratic advance of the electrode 2. in the most extreme situation, when the electrode bores through the bottom face of the workpiece 6 and allows direct escape of electrolyte, the effective electrolyte pressure at the gap region falls abruptly, and the load compensating means, no longer balanced by the electrolyte reaction force, tends to push the electrode against the workpiece by driving it forward with sudden surge which is independent of the slow forward motion caused by the drive means, This happens because the electrode usually breaks through the bottom of the workpiece at a localized region so that the hole is not full-size to permit the electrode to pass through without touching the workpiece. Typically, the normal gap clearance between the electrode and the workpiece is small, and upon release of the electrolyte pressure at the gap, the resilience of the drive mechanism, and the play in the drive parts, allows the electrode to jump forward into damaging contact with the workpiece when urged by the load compensating means.

In the drive system, there is shown a main guide housing 18 of elongated cylindrical open-ended form, a ram 19 slidably mounted therein and projecting through the open end thereof, and an enlarged ram head 20 carried externally on the ram and secured to the adapter plate 17. The main'housing 18 is fitted with a sleeve bushing 21 within its open end for slidable guiding engagement with the ram shaft 19 and housing 18 is also fitted with a radial bearing 22 and an intermediate thrust bearing 23 rotatably mounting the end and intermediate journal portions of a drivescrew 24. A collapsible protective boot 25 of bellows form is anchored between the ram head 20 and the guide housing 18 to enclose and protect the exposed portion of the ram shaft 19. The ram shaft 19 has a stepped diameter axial bore 198 forming a mounting socket for drive nut 26 that cooperates with the drive screw to advance and retract the ram head 20.

A drive motor 27 is shown with a shaft 278 carrying a the drivescrew shaft. A suitable link chain 30 is shown trained about the sprockets 28, 29 and an electric brake 31 is shown within the guide housing 18 to engage the extreme end of the drive shaft.

In normal operation, the motor 27 drives the ram head 20 to advance it at a constant rate of speed during machining operations, or to retract it, the drive being from the sprocket 28, through the chain 30 to the sprocket 29 to rotate the drivescrew 24. The drive nut 26 is fixed within the ram shaft to control the ram shaft 19 in accordance with the speed and direction of rotation of the drivescrew.

Electrolyte is supplied through the feed line 9 to the feed bushing 10 and flows across the gap between the workpiece 6 and the electrode 2, and then through the electrode 2 and holder 4 to the return line 12. The electrolyte pressure at the gap and acting on the differential area presented by the electrode and electrode holder is determined by the pump P and typically may be about 250-300 p.s.i. A direct current power source is represented at 32 and is shown connected to the workpiece 6 and the electrode holder 4 in a sense to make the workpiece anodic and the shaping electrode cathodic.

As described thus far, the shaping cathode is arranged to sink a hole in the workpiece. Current flow across the electrolyte gap between the shaping cathode and the workpiece removes metal from the workpiece as the drive system advances the electrode. it is desirable that the drive system not be subjected to the high opposing reaction force which may be present with large work areas. it is also desirable that the drive system be capable of adapting to rapid changes in electrolyte pressure to prevent surges in the movement of the drive system.

in accordance with the present invention, a load-compensating system is associated with the ram head 20 to develop hydrostatic forces assisting advance of the ram head to at least partially counteract the reaction force occasioned by the highpressure electrolyte acting at the gap region. A balanced array of hydraulic piston and cylinder mechanisms each designated generally at 33 is shown connected directly to the ram head 20 to assist its advance. Each mechanism, as shown for purposes of illustrative disclosure, has a single ended piston 34 and piston rod 35 in rigid driving engagement with the ram head 20 and a cylinder 36 housing the piston and defining a pressure chamber 37 therefor.

Hydraulic pressure is applied to the pressure chambers 37 to produce a compensating force proportional to the reaction force. The relationships of pressure and area in the hydraulic mechanisms 33 are generally selected to partially compensate for the reaction force caused by pressurized electrolyte in the gap region so that the drive system is subjected to a reduced unbalanced reaction force resulting from electrolyte pressure.

In the particular arrangement disclosed herein, the electrolyte feed system has a branch line 38 leading from the discharge side of the pump P and connected to the pressure chambers 37 to utilize electrolyte at the actual feed system pressure as the actuating medium for the hydraulic compensators 33. Any changes in the electrolyte pressure occur substantially simultaneously at the gap region and in the compensating chambers 37, so that such changes automatically cancel out and do not present surge conditions to the drive. For example, when the shaping electrode 2 breaks out through the rear face of the workpiece, the close clearance gap conditions and the throughflow electrolyte path are disrupted and there is a sudden drop in pressure at the gap region with a consequent sudden drop in the electrolyte reaction force on the ram head 20. This drop in electrolyte pressure is immediately reflected in a loss of pressure at the discharge side of the pump P so that the pressure acting in the chambers 37 of the hydraulic mechanisms also drops proportionately, to maintain the desired balance of forces at'the ram head and thereby prevent contact with the workpiece. Other changes in system pressures due to variation in pump output pressure or for other reasons are reflected rapidly between these regions to maintain the desired balance and allow the drive system to determine and maintain a uniform and steady advancing movement of the electrode.

Another embodiment of the invention is shown in FIG. 2 for producing a compensating force that partially counteracts the reaction force occasioned by the electrolyte pressure acting on the area presented by the electrode and holder assembly. Corresponding reference characters in the l00 series are used to identify corresponding parts.

Accordingly, in FIG. 2, a hollow shaping electrode 102 is carried by a hollow holder or cathode-mounting means 104 to be advanced toward a conductive workpiece 106 to maintain a narrow gap therebetween. A pressurized liquid electrolyte supply system for maintaining electrolyte flow at the gap in cludes a storage container 108, a feed line 109 equipped with a pressure pump P and leading into the upper end of the electrode holder 104. A splash shield 110 is shown contacting the workpiece 106 and encircling the holder 104 to accommodate relative advancing and retracting movement of the electrode and holder assembly. A return line 112 is shown leading from the splash shield 110 to complete the electrolyte flow path which, in this embodiment, is shown to extend forwardly through the holder 104 and the electrode 102, then out of the electrode and through the work gap between the electrode and the workpiece.

The drive mechanism for the electrode assembly, designated generally at 114, includes a pair of adapter plates 116, 117, the plate 116 being of any suitable electrically insulating material mounted in thrust relation to the end of the holder 104. In this system, the differential area exposed to electrolyte pressure by the electrode assembly again results in a high opposing reaction force action to resist steady advance of the electrode by the drive mechanism toward the workpiece. A typical load-compensating system is shown herein to partially balance out these electrolyte reaction forces and allow the drive system to effect a uniform advance of the electrode. However, variations in electrolyte pressure at the gap region, whether caused by supply pressure variations or by breakthrough of the electrode through the workpiece or by other environmental changes in the electrolyte flow, impose transient demands upon the drive 114 leading to erratic advance of the electrode unless the load-compensating system instantaneously balances such variations.

in the drive system disclosed in FIG. 2, there is shown a main guide housing 118 (represented only fragmentally) and a ram 119 shiftably mounted therein. Ram 119 includes a ramhead 120 projecting through the lower end thereof, and is guided by antifriction bearing elements 121 mounted within the guide housing 118. A drivescrew 124 engages a drive nut 126 carried in the upper end ofthe ram, the upper end of the drivescrew being shown projecting through a thrust bearing 123 shown mounted on a frame structure 1231-".

A drive motor 127 is shown powering a variable speed drive 127V and a gear reducer unit 127R to rotate a drive sprocket 128 for powering a sprocket 129 by means ofa link chain 130. The sprocket 129 is mounted directly on the upper end of the drivescrew 124.

The load-compensating system 115 includes a pair of hydraulic mechanisms 133 each of which comprises a singleended piston 134 and piston rod 135 that is in rigid driving engagement with the ramhead 120, and a cylinder 136 housing the piston and defining a pressure chamber 137 therefor. Hydraulic pressure is applied to the pressure chambers 137 through a feed line 138 from a recycling hydraulic fluid system 139, the feed line 138 being shown with a supply valve 140.

The hydraulic-recycling system 139 includes a storage tank 141, a discharge line 142 leading from the bottom of the tank 141 and equipped with a hydraulic fluid prescribed pump P and a return line 143 leading to the storage tank and equipped with an adjustable pressure-regulating valve 144. Thus, the pressure maintained in the recycling system is selectively adjustable to provide control of the pressure acting on the pistons 134 and thereby acting to assist advance of the ramhead 120. Typically, the pressure and area relationships established in the compensating system 115 provide a compensating force to partially neutralize the opposing reaction force caused by pressurized electrolyte in the gap region. Thus, the load seen by the drive is limited to a range at which the drive system can produce a uniform advance of the electrode. Exact balance between the reaction force and the compensating force is not necessary so long as the load on the drive system is not excessive.

1n the disclosed arrangement, the drive system load is monitored, and automatic adjustment of the hydraulic pressure is effected to maintain the drive system load within a prescribed range. For this purpose, a strain gauge 145 of any suitable type is mounted upon a transverse support arm 123A of the frame 123F to sense bending strain produced on the arm 123A by the effective drive system load. The strain gauge controls the operation of an amplifier 146 which governs the setting of the adjustable pressure regulating valve 144.

When the bending strain sensed by the gauge rises due to an increased electrolyte back pressure, the amplifier 146 progressively throttles the valve 144 to increase the pressure in the hydraulic-recycling system and correspondingly to increase the compensating force applied through the piston rods 135. When the bending strain drops below a predetermined minimum valve, indicative of overcompensation, the gauge 145 signals the amplifier 146 to open the valve 144 to effect a reduction of pressure in the hydraulic-recycling system and allow the drive system to accept its normal load.

A direct current power source is represented at 132 and is shown connected to the workpiece 106 and the electrode holder 104 in a sense to make the workpiece anodic and the exposed end face of the electrode cathodic.

In the general operation of the system, current flow is maintained through the pressurized electrolyte at the gap to erode the workpiece as the cavity sinking electrode 102 advances. During this action, the high reaction forces associated with the high electrolyte pressures required for efficient demetallizing are partially balanced by the compensating force applied through the hydraulic mechanisms 133. Continuous control over the compensating action is effected by the strain gauge 145 and amplifier 146.

While the described system is effective for maintaining a steady advance of the electrode in the presence of minor or gradual variations in electrolyte pressure, sudden and significant pressure drops require a more rapid compensating system response. When the electrode breaks through the remote face of the workpiece, a sudden drop in the electrolyte back pressure results due to the interruption of the electrolyte throughflow path. The compensating force would immediately predominate and push the electrode against the workpiece to the damage of both parts, before an adjusting response through the strain gauge, amplifier and pressure valve system could occur.

In accordance with the present invention, sudden drops in electrolyte pressure are directly sensed, and controls are provided for directly and rapidly reducing the hydraulic pressure acting in the compensating system. For this purpose, a pressure sensitive transducer such as a piezoelectric element 147 (protected, of course, from corrosion by electrolyte) is mounted within the electrode holder 104 upstream of the work gap to be exposed to the electrolyte pressure in the stream of electrolyte flowing to the gap and to produce a control signal proportional to such pressure. The hydraulic compensating system has exhaust lines 148 leading from the cylinders 136 and equipped with pressure relief valves 149. Control signals from the transducer 147 are applied through a control circuit 150 adapted to pass rapid signal changes but not slow signal changes. Control circuit 150 is connected by control wires 151 to effect rapid opening of relief valves 149, in response to a rapid signal change from transducer 147, to relieve hydraulic pressure from the load-compensating system immediately upon sudden loss of electrolyte pressure at the transducer.

The relief of hydraulic pressure precludes any sudden forward thrust of the electrode, thereby preventing damaging impact with the workpiece. The sudden loss of pressure due to workpiece breakthrough usually occurs before the cavity is completely cleared of workpiece material. Upon loss of electrolyte pressure, the drive balance is restored by immediately relieving the hydraulic pressure on the compensating system, and the main drive system 114 continues its steady advance of the electrode accompanied by final erosion of the workpiece, all without any contact with the workpiece.

FIGS. 3 and 4 disclose another embodiment of the apparatus of this invention, which has a large electrode capable of being moved by a drive mechanism into a workpiece at a which also has load-compensating means for partially neutralizing the retractive force generated by pressurized electrolyte located between the electrode and the workpiece. The load-compensating means comprises a chamber at the rear of the electrode into which pressurized fluid can be admitted to pressurize the back of the electrode, providing load-compensating force to neutralize a portion of the retractive force.

Electrode 201 is shown to be a large plate having a threedimensional contour to its bottom surface. This type of electrode is typically used to prepare large dies having a contour to their working surface of shape generally complementary to the contour of the lower surface of the particular electrode used.

Electrode 201 is shown in adjacent relation with workpiece 203 which is shown already shaped by electrode 201 through operation of the apparatus. The workpiece rests on table 204, and is surrounded by insulating spacer 205, which has a central space in which the workpiece closely fits to form a sealing contact. Spacer 205, in turn, abuts sealingly against wall 207 which serves as a position locating means for the workpiece along one horizontal axis, while one or more pins 208 (seen in FIG. 4) serve to locate the workpiece along a second horizontal axis. Thus, workpiece 203 can be precisely positioned under the electrode by simply abutting it against wall 207 and pins 208.

Sockets 210 are used to hold pins 208. Only one socket 210 is shown in use, the remaining sockets being put to use when it is desired to position a workpiece of different size or to position a workpiece at a different location.

In the embodiment shown, the workpiece is sufficiently large and heavy so that no means for positively holding it in one position is required. The workpiece is held against table 204 not only by its own weight but also by the force of the electrostatic pressure of the electrolyte in the work gap, backed by the ram means that pushes the shaping cathode toward the workpiece. For the reasons indicated, it is not necessary (as in Mikoshiba et al. U.S. Pat. No. 3,399,l25, for example) to provide protuberances on the workpiece through which it can be bolted in place while it is electrochemically modified.

Table 204 carries conventional airlift devices 211 to facilitate the sliding of workpiece 203 on and off table 204. pushrod pushrod Electrode 201 is held by adapter plate 212, which, in turn, is carried by electrode mount 213, to constitute a cathode member. Apertured plate 214 is held between plate 212 and mount 213. Mount 213 is stiffened and rendered inflexible by a plurality of vertical fins 215 which extend from the mount 213 to pushrod 217, which is shown to be an integral part of mount 213. The horizontal area of pushrod 217 is substantially less than the horizontal area of mount 213 for a reason explained below.

A ramhead 219 is affixed to the top of pushrod 217, and ramhead 219 is in turn affixed to a conventional ram (not shown), which is typically operated in the manner of FIGS. 1 or 2 by a drive screw, a thrust bearing, and a motor to provide a uniform rate of advance of the electrode 201 toward the workpiece 203 during electrochemical machining.

While only one pushrod 217 is shown in this embodiment, it is contemplated that a plurality of pushrods can be used in this invention to engage electrode mount 213 so that the electrode can be advanced with a minimum of bending due to electrolyte back pressure. A plurality of pushrods would desirably be used in cases where electrode 210 and mount 213 are of exceptionally large area.

Cover 221 surrounds pushrod 217 and is affixed to wall 207 and other supports 223, typically by bolts, to define a pressure chamber 225 in cooperation with the back side 226 of electrode mount 213. Stress members 222 limit bulging of the cover when chamber 225 is heavily pressurized. Pushrod 217 extends through an aperture in the top of cover 221 in sliding relation thereto to permit pushrod 217, mount 213, and electrode 201 to be raised and lowered with respect to cover 221 and the workpiece 203.

Plungers 227 can be inserted into recesses 229 in pushrod V 217 to hold the pushrod 217 and cover 221 together. The cover 221 can then be unbolted from wall 207 and supports 223, and the pushrod and cover can be raised together to obtain access to the workpiece 203.

In the embodiment shown in FIGS. 3 and 4, pressurized electrolyte is fed through inlets 231, passing through the region 233 between electrode 201 and insulating spacer 205, and from there passing to work gap 235 between electrode 201 and workpiece 203. The pressurized electrolyte is drained from the work gap 235 by electrolyte flow channels which comprise slots 236, some of which lead into chambers 237. The electrolyte passes into slots 236, through electrode 201, and into horizontal channels 239 (best seen in FIG. 4) in the adapter plate 212. Channels 239 are closed at their ends.

The pressurized electrolyte passes along horizontal channels 239 to a point underneath an aperture 216 in plate 214. The electrolyte then flows through apertures 216 into one of a plurality of radial channels 241, formed in the interior of electrode mount 213, and which pass over horizontal channels 239. The electrolyte then passes from radial channels 241 into vertical channels 243 in pushrod 217 and out of the device by exit ports 245. In the disclosed embodiment, eight radial channels 241 diverge in an equiangular manner out from pushrod 217 to pass over horizontal channels 239.

If desired, the apertures 216 in plate 214 can be so arranged that electrolyte flowing into slots 236 in high areas 255 of electrode 201 (see FIG. 3) is transported to different radial channels 241 and vertical channels 243 than the electrolyte flowing into slots 236 which are located in low areas 257 of the electrode.

The advantage of this is that the channels 243 which carry electrolyte from slots 236 located in low areas 257 of the electrode can then be blocked to prevent the flow of electrolyte during the initial stage of electrolytic machining, before the workpiece has substantially assumed the configuration of the working face of the electrode.

The reason that this is desirable is that, in the initial stage. high areas 255 are in close proximity with the workpiece 203, but low areas 257 are not, leaving wide spaces at various places between the electrode and the workpiece. Depending upon the configuration of the electrode, it is possible that wide channels between the electrode and the workpiece can become accessible to the electrolyte to permit it to flow through the electrode and out of the apparatus without being forced under high pressure between the narrow work gap 235, which at this point exists only in the vicinity of high areas 255. This can cause the electrolyte pressure to drop substantially, interfering with the operation of the apparatus.

To counteract this, the above modification can be used in conjunction with valves to close those vertical channels 243 which connect with slots 236 in the low areas 257 of the electrode, to prevent the flow of electrolyte therethrough. After sufficient from moving demetallization has taken place in the vicinity of high areas 255 to cause the workpiece to assume the general configuration of electrode 201, the valves are opened to permit electrolyte to flow through slots 236 in low areas 257. Electrolytic demetallization then takes place uniformly over the entire working face of the electrode.

Pressurized electrolyte which is passed into the apparatus by inlets 231 also passes into pressure chamber 225 via the passage 246 defined between the periphery of adapter plate 212 and electrode mount 213, and cover 221. Pressurized electrolyte is prevented from escaping chamber 225 between pushrod 217 and the wall of the aperture in cover 221 through which rod 217 passes by annular seal 247. Seal 247 is carried by cover 221 and surrounds pushrod 217, providing a pressure seal through which the pushrod can slide. A seal to prevent the escape of electrolyte can also be placed between the bottom inner portion of cover 221 and insulating spacer 205.

Thus, as pressurized electrolyte is provided to the work gap 235 to permit the flow of electric current between electrode 201 and workpiece 203 for demetallizing and shaping the workpiece, pressurized electrolyte also flows into chamber 225. The back pressure against electrode 201 which is created by pressurized electrolyte in work gap 235 is thus partially neutralized by a forward pressure exerted on back 226 of the electrode mount 213 by pressurized electrolyte in chamber 225. The resulting back pressure which is sensed by pushrod 217 and the drive means for the rod is theoretically the product of the mean pressure of the electrolyte in work gap 235 multiplied by the transverse area of pushrod 217, since the back pressure of electrolyte in work gap 235 against the remaining area of electrode 201 and the other parts exposed to electrolyte back pressure is counterbalanced by the electrolyte pressure on back 226 of the electrode mount.

In the event of a change in electrolyte pressure in the system, caused, for example, by a failing or shutting off of the pump used to provide pressurized electrolyte, the drop in electrolyte pressure at the work gap 235 and chamber 225 takes place in an essentially simultaneous manner, since there is an electrolyte conduit permitting free flow of electrolyte between the two regions. Thus, the danger that a drop in pressure at the work gap may cause the load-compensating means to overbalance the system and drive the electrode 201 into damaging contact with workpiece 203 is essentially eliminated.

Direct electric current passes through the apparatus in a sense to make electrode 201 cathodic with respect to workpiece 203. Cables 249 and 251 (shown in FIG. 4) connect the apparatus with a source of electric current. The current passes between the cables by way of table 204, workpiece 203, work gap 235 through which pressurized electrolyte passes, electrode 201, plates 212 and 214, mount 213, pushrod 217, and ram head 219.

The underside of table 204 is shown to be covered with an insulating pad 253 to prevent short circuits, and the top of ram head 219 typically contains a similar insulating pad (not shown) to prevent the passage of electric current into the ram and drive means. Other insulating members are spacer 205, wall 207, and supports 223, which prevent the direct flow of electric current between table 204 and cover 221, limiting the current flow path of travel through workpiece 203 and work gap 235. The insulating members used herein can typically be made ofcomposites of epoxy resin and glass fiber.

Another embodiment of this invention is shown in FIGS. 5 through 7. The basic plan and function of the apparatus shown therein is similar to the apparatus of FIGS. 3 and 4, except that the electrolyte flow path is somewhat different. Corresponding reference characters in the 300" series are used to identify corresponding parts.

Electrode 301 is shown in adjacent relation to workpiece 303, which is shown in an advanced stage of electrolytic machining, wherein the upper surface of workpiece 303 conforms to the lower surface of electrode 301. workpiece 303 rests upon table 304, and the workpiece is surrounded by insulating spacer 305.

Electrode 301 is held by adapter plate 312 to electrode mount 313, with apertured plate 314 mounted between them. Mount 313 is carried by pushrod 317, which extends through an aperture (not shown) in cover 321 to define a pressure chamber 325. As in the embodiment of FIGS. 3 and 4, pressurized electrolyte is permitted to flow into pressure chamber 325 to press against the back 326 of electrode mount 313 to partially neutralize the retractive force created by pressurized electrolyte at the work gap 335 between electrode 301 and workpiece 303.

Pressurized electrolyte enters the apparatus of FIGS. 5 through 7 at inlet 331 to pass into chamber 325 and also to pass horizontally above spacer 305 into the loop-shaped passage 346 between adapter plate 312 and cover 321. Electrolyte also passes into the outer portions of work gap 335.

The electrode of this embodiment has alternating slots 336a and b and outlets 337, while the adapter plate 312 has alternating horizontal channels 339a and b. Channels 33% only lead under apertures 316 in plate 314 to permit flow of elec trolyte between each horizontal channel 33% and radial channel 341, which, in turn, leads into a vertical channel 343. There is no aperture connecting channels 339a with radial channels 341.

As described above, the apparatus of FIGS. 5 and 6 is quite similar to the apparatus of FIGS. 3 and 4, differing primarily in the arrangement of apertures 316 in plate 314. A major difference between this and the previous embodiment is that horizontal channels 339a in this embodiment pass through the sidewall of adapter plate 312 to define electrolyte entry ports 344 (shown in FIG. 6) for receiving pressurized electrolyte with occupies the passage 346 (shown in FIG. 5) between adapter plate 312 and cover 321. The pressurized electrolyte flows into the horizontal channels 3390 from entry ports 344, the electrolyte flowing along channels 339a and then downwardly and out slots 336a into the work gap 335. The slots 3360 thus constitute electrolyte inlet channels.

The elctrolyte then migrates along the work gap 335 to a slot 336b in the electrode which serves as an outlet channel for the electrolyte from the work gap. The electrolyte passes upwardly through these slots, through chambers 337, to one of horizontal channels 339b, along which it passes until it encounters an aperture 316 in plate 314, flowing through the aperture into a radial channel 341. From there it flows into a vertical channel 343 and out of the apparatus.

Thus, this embodiment of the apparatus provides an electrolytic machining apparatus in which the electrolyte is both fed into and removed from the work gap by electrolyte channels which lead through the electrode. An advantage of this is that electrolyte is provided to work gap 335 at points distributed across the face of electrode 301, rather than only at the periphery as in the embodiment of FIGS. 3 and 4. This reduces the possibility of an electrolyte shortage at the center of the work gap 335.

In another embodiment of the apparatus of this invention, insulating spacer 305 can be modified to tightly fit against the side of electrode 301, to prevent fluid flow between inlets 331 and work gap 335. Electrolyte entry ports 344 are also sealed. The apertures 316 in plate 314 can be so arranged in conjunction with radial channels 341 and horizontal channels 339 that electrolyte can be pumped down some of the vertical channels 343 (shown in FIG. 6) to pass out some of the slots 336 in the electrode, passing across work gap 335 to be collected in other slots 336. The electrolyte then passes into other horizontal channels 339, radial channels 341, and vertical channels 343, and out of the apparatus.

Two separate pressurized fluid systems are used in this particular embodiment, one consisting of pressurized electrolyte flowing to and from the work gap 335 via separate vertical channels 343 in the pushrod 317, and the other system consisting of electrolyte or another fluid passing through inlet 331 into chamber 325 to provide load compensating force to the back 326 to the electrode.

In this embodiment, a separate control system is generally required to rapidly cut off the pressure of the fluid in chamber 325 upon a drop in the pressure of the electrolyte at work gap 335 in order to prevent electrode 301 from moving forward into damaging contact with workpiece 303 upon a drop in electrolyte pressure at the work gap 335. This can be accomplished through the use of a valve in cover 321 connected to a pressure sensing means, similar to the arrangement shown in FIG. 2.

Another embodiment of this invention is shown in FIGS. 8 aNd 9. The basic plan and function of the apparatus shown in those figures is similar to the apparatus of FIGS. 3 and 4, with the additional feature that electrolyte that leaks through the seal between the workpiece and the insulation spacer lying between it and the cover means is drained off so the electrolyte will not be forced between the workpiece and the table on which it is supported. Corresponding reference characters in the 400 series are used to identify corresponding parts.

Electrode 401 is shown in adjacent relation to workpiece 403,

which is shown in an advanced stage of electrochemical,

machining, wherein the upper surface of workpiece 403 conforms to the lower surface of electrode 401.

workpiece 403 rests upon workpiece carrying mount or table 404, and the workpiece is surrounded by insulating spacer 405. The inner wall of spacer 405 is shown in sealing contact with the outer wall of workpiece 403, and the outer wall of the spacer is in sealing contact with the bottom inner portion of cover 421. The first mentioned seal is strengthened by means of O-rings 402, and the second seal is strengthened by means of O-rings 406.

The upper surface of table 404 is complementary in shape to the bottom surface of workpiece 403, so that these two members also form a sealing contact.

Electrode 401 is held by adapter plate 412 to electrode mount 413, with apertured plate 414 mounted between them. Mount 413 is carried by pushrod 417, which extends through an aperture in cover 421 to define a pressure chamber 425. As in the embodiment of FIGS. 3 and 4, pressurized electrolyte is permitted to flow into pressure chamber 425 to press against the back 426 of electrode mount 413 to partially neutralize the retractive force created by pressurized electrolyte at the work gap 435 between electrode 401 and workpiece 403.

Pressurized electrolyte enters the apparatus of F lGS. 8 and 9 at inlet 431 to pass into chamber 425 and also to pass above insulating spacer 405 into the loop-shaped passage 446 between adapter plate 412 and cover 421, and from there into chamber 425. Pressurized electrolyte fed through inlets 431 also passes through the region 433 between electrode 401 and insulating spacer 405, and from there passes to work gap 435 between electrode 401 and workpiece 403.

The pressurized electrolyte is drained from the work gap 435 by electrolyte flow channels which comprise slots 436, some of which lead into chambers 437. The electrolyte passes into slots 436, through electrode 401, and into horizontal channels 439 (best seen in FIG. 9) in the adapter plate 412. Channels 439 are closed at their ends.

The pressurized electrolyte passes along horizontal channels 439 to a point underneath an aperture 416 in plate 414. The electrolyte then flows through apertures 416 into one of a plurality of radial channels 441, formed in the interior of electrode mount 413, and which pass over horizontal channels 439. The electrolyte then passes from radial channels 441 into vertical channels 443 in pushrod 417 and out of the device by exit ports at the top of the pushrod.

Direct electric current passes through the apparatus in a sense to make electrode 401 cathodic with respect to workpiece 403. Cable 449 (shown in FIG. 9) connects worktable 404 with a source of electric current, and a similar cable 451 connects the top of pushrod 417 to the current source. The current passes between the cables by way of table 404, workpiece 403, work gap 435 through which pressurized electrolyte passes, electrode 401, plates 412 and 414, mount 413, and pushrod 417.

The underside of table 404 is shown to be covered with an insulating pad 453 to prevent short circuits. insulating sheet 454 is provided around the periphery of the top of table 404 to prevent stray etching of the table. Other insulating members are spacer 405 (described above) and backup wall 407, which prevent the direct flow of electric current between table 404 and cover 421, limiting the current flow path to travel through workpiece 403 and work gap 435.

As pointed out above, electrochemical machining proceeds most effectively when the electrolyte flows through the work gap between the workpiece and the shaping cathode at a relatively high pressure, frequently 200 p.s.i. or above. This means that electrolyte introduced through inlets 431 presses down with a large force on upper surface 456 of insulating spacer 405, and similarly presses down on the upper surface of workpiece 403. Because of the high pressures involved, some leakage of electrolyte from regions 433 down through the seal formed between the outer wall of the workpiece and the inner wall of insulating spacer 405 is usually unavoidable.

Some of this leaking electrolyte tends to work its way down to the bottom of the interface between workpiece 403 and insulating spacer 405. A pressure buildup results at the bottom of that interface, which may involve a pressure greater than the pressure in work gap 435 if there is a drop in the pressure in that work gap, as sometimes occurs during the electrochemical machining process. if this situation develops, the electrolyte that has leaked down as described will then be forced into the seal between the bottom face of workpiece 403 and the complementary upper surface of workpiece carrying amount or table 404.

The leaking of electrolyte under pressure in the manner just described raises workpiece 403 off table 404, and may in addition cause the workpiece to shift laterally from its desired position if there is any appreciable play in the seal between the workpiece outer wall and the spacer inner wall. Either a vertical lifting or a lateral shifting will of course impair the accuracy of the cut in the machining process, and should be avoided if at all possible.

in the embodiment of FIGS. 8 and 9, undesirable leaking of electrolyte under pressure between workpiece 403 and table 404 is avoided by providing at least one drain passage through insulating spacer 405 from the interface between the workpiece and the insulating spacer, which drain passage leads to a zone having a fluid pressure lower than that in sealed chamber 425 and regions 433. in the embodiment shown, a plurality of drain holes 460 are provided through the sides of spacer 405 at the left and right of FIG. 8. Drain holes 460 are all connected by collecting groove 462, which extends around the entire inner perimeter of spacer 405.

Electrolyte which leaks from regions 433 down between workpiece 403 and spacer 405 is collected in groove 462, and passes from there through drain holes 460. This electrolyte is received in collecting groove 464 in the inner wall of backup member 407. As shown, collecting groove 464 extends along the left and right sides of the apparatus shown in FIG. 8. it may be formed, if desired, in the outer wall of spacer 405, or partly in that wall and partly in the inner wall of backup member 407. In any case, collecting groove 464 is defined by said two walls.

Electrolyte is led from collecting groove 464 to the atmosphere through drain passages 466 which pass through wall 407. in the embodiments shown, passages 466 are fewer in number than drain holes 460, and are spaced differently from those drain holes. Electrolyte that is discharged from drain holes 466 falls to the floor of the enclosure of the apparatus, and from there is channeled back to the supply tank.

STill another escape route is provided for electrolyte that leaks through the seal between workpiece 403 and spacer 405, in the form of drain grooves at the bottom of member 405. As shown in FIG. 8, electrolyte that leaks below bottom O-ring 402 is accumulated in collecting groove 468 that extends entirely around the bottom inner portion of spacer 405. From this collecting groove, electrolyte passes through drain groove 470 in the bottom surface of spacer 405. The bottom of spacer member 405 is otherwise complementary in shape to the upper surface of table or workpiece carrying mount 404.

Electrolyte emerging through drain grooves 470 is accumulated in collecting groove 472, which may be located in either the outer wall of spacer 405 or the inner wall of backup member 407, or partly in each wall. in any case, the groove is defined by both said walls. in the embodiments shown, collecting groove 472 is formed in the bottom outer portion of spacer 405, and extends around the entire perimeter of the spacer.

Electrolyte that accumulates in collecting groove 472 passes through drain grooves 474 in the bottom of backup wall 407. 'DRain grooves 474 are positioned in spaced locations different from the locations of drain grooves 470. When electrolyte emerges from drain grooves 474, it falls to the floor of the enclosure and is channeled back to the supply tank.

As a result of the arrangement of drain passages described, both spacer 405 and workpiece 403 are pressed firmly against table 404 regardless of any electrolyte that may leak down between those two members and tend to seep between the workpiece and mounting table 404. The downward electrolyte pressure on the top surface of spacer 405 is unopposed by any upward pressure on the bottom of that member because of the drain grooves that communicate with the atmosphere. For the same reason, the downward pressure of the electrolyte in work gap 435 is unopposed by electrolyte pressure in an upward direction upon the bottom of workpiece 403, because any electrolyte that leaks down to the bottom of the interface between spacer 405 and the workpiece is in communication through drain grooves 470 with the atmosphere.

From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the true spirit and scope of the novel concept of the invention. it is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.

What is claimed is:

1. An apparatus for electrochemically machining an electrically conductive and electrochemically erodable workpiece having an outer wall and a bottom surface which comprises: a mount for carrying said workpiece, said mount having an upper surface complementary in shape to said bottom surface of the workpiece; a shaping cathode member mounted at an end of at least one pushrod, said shaping cathode member having a face and a back surface, the cross-sectional area of said cathode member taken through a plane perpendicular to the axis of said pushrod being substantially greater than the same total cross-sectional area of all said pushrods; drive means to move said pushrods in a direction generally parallel to the axis of said pushrods to bring the face of said cathode into close proximity with a workpiece carried by said mount to define a work gap between said cathode and workpiece, and to advance the cathode into the workpiece; means for passing a stream of pressurized liquid electrolyte through said work gap, whereby a relative retractive force is exerted between the face of said cathode and the workpiece when pressurized electrolyte is passed through said work gap; cover means to enclose said cathode member and workpiece, and to define a sealed chamber behind the back surface of said cathode member, said cover means including a spacer formed of insulating material, said spacer having an inner wall adapted to be in sealing contact with said outer wall of the workpiece and a second wall in sealing contact with the remainder of said cover means, said cathode member being movable with respect to said cover means; means for supplying pressurized fluid to said chamber to exert pressure against said cathode back surface for at least partially counteracting said relative retractive force; means responsive to the pressure in said work gap to control the pressure of said fluid supplied to said chamber and to maintain said pressure exerted against said cathode back surface in generally proportional relation to the pressure in said work gap; and means for passing direct electric current between said cathode face and said workpiece in a sense to make the workpiece anodic, said insulating spacer having at least one drain passage therethrough leading from the interface between its inner wall and the outer wall of the workpiece to a zone having a fluid pressure lower than that in said sealed chamber, whereby pressurized electrolyte that may leak through the seal between the spacer and workpiece can escape through said drain passage to said zone of lower fluid pressure instead of being forced between the lower surface of the workpiece and the upper surface of said mount.

2. The apparatus of claim 1 in which the inner wall of said insulating spacer defines a collecting groove that extends around the perimeter of said spacer and communicates with said drain passage that passes through the spacer.

3. The apparatus of claim 1 in which said insulating spacer has a bottom surface generally complementary to the upper surface of said mount, said bottom surface defining at least one drain groove that extends from the interface between the spacer and workpiece to a zone having a fluid pressure lower than that in said sealed chamber.

4. The apparatus of claim 3 in which the bottom surface of the insulating spacer has a plurality of drain grooves as there defined, said drain grooves being interconnected by a collecting groove in the inner wall of said spacer, and in which said spacer also has a plurality of drain holes therethrough, said drain holes being interconnected by a collecting groove in the inner wall of said spacer, all said drain grooves and drain holes being in communication with the atmosphere.

5. The apparatus of claim 1 which includes a backup wall surrounding said insulating spacer, said backup wall having at least one drain passage therethrough that connects the drain passage that passes through the insulating spacer with a zone having a fluid pressure lower than that in said sealed chamber.

6. The apparatus of claim 4 which includes a backup wall surrounding said insulating spacer, said backup wall having a plurality of drain passages therethrough that connect said drain grooves and drain holes in the spacer with the atmosphere.

7. The apparatus of claim 6 in which said drain passages in the backup wall are spaced differently from said plurality of drain grooves and said plurality of drain holes in the insulating spacer, said drain grooves in the spacer being connected with drain passages through the backup wall by means of a collecting groove defined by the outer surface of the spacer and the inner surface of the backup wall, and said drain holes in the spacer being connected with drain passages through the backup wall by means of a collecting groove defined by the outer surface of the spacer and the inner surface of the backup wall, the drain passages through the backup wall being in communication with the atmosphere.

8. An apparatus for electrolytically machining an electrically conductive and electrochemically erodable workpiece which comprises: a mount for carrying a workpiece; a shaping cathode member; at least one pushrod having said cathode member mounted at an end thereof, said shaping cathode member having a face and a back surface, the cross-sectional area of said cathode member taken through a plane perpendicular to the axis of said pushrod being substantially greater than the same total cross-sectional area of all said pushrods; drive means to move said at least one pushrod in a direction generally parallel to the axis thereof to bring the face of said cathode into close proximity with a workpiece carried by said mount to define a work gap between said cathode and workpiece, and to advance the cathode into the workpiece; means for passing a stream of pressurized liquid electrolyte through said work gap, whereby a relative retractive force is exerted between the face of said cathode and the workpiece when pressurized electrolyte is passed through said work gap; cover means to enclose said cathode member and workpiece, said cathode member being movable with respect to said cover means; an insulating spacer between said cover means and workpiece and cooperating therewith to define a sealed chamber behind the back surface of said cathode member; means for supplying pressurized fluid to said chamber to exert pressure against said cathode back surface for at least partially counteracting said relative retractive force; means responsive to the pressure in said work gap to control the pressure of said fluid supplied to said chamber and to maintain said pressure exerted against said cathode back surface in generally proportional relation to the pressure in said work gap; and means for passing direct electric current between said cathode face and said workpiece in a sense to make the workpiece anodic.

9. The apparatus of claim 8 in which a plurality of electrolyte flow channels lead through said cathode member, between said work gap and the exterior of the apparatus, and in which some of said electrolyte flow channels constitute electrolyte inlet channels while some of said electrolyte flow channels constitute electrolyte outlet channels with respect to said work area.

10. The apparatus of claim 9 in which an electrolyte conduit forms an open path between said chamber and work gap to permit the flow of electrolyte therebetween.

ll. The apparatus of claim in which electrolyte passes through said work gap via an electrolyte flow path including at least a portion of said electrolyte conduit and including said electrolyte flow channels which lead through said cathode member.

12. The apparatus of claim 11 in which said cathode face is a three-dimensional surface having high areas and low areas, said high areas generally coming into close proximity with a flat workpiece before the low areas as said cathode face and said workpiece are moved together; some of said electrolyte channels leading from said work area through said high areas, and some of said electrolyte channels leading from said work area through said low areas; said apparatus having means for blocking electrolyte flow through said electrolyte flow channels which lead through said low areas until electrolytic machining has proceeded in the workpiece to such a degree that said low areas are in close proximity to said workpiece.

13. The apparatus of claim 8, including the further improvement of means defining a plurality of outlet flow channels through said cathode member and a plurality of inlet flow channels between said cathode member and said workpiece.

14. The apparatus of claim 8 in which said cathode member is mounted on a single pushrod member.

15. The apparatus of claim 8 in which said cathode member is mounted on a plurality of pushrod members.

16. An apparatus for electrolytically machining an electrically conductive and electrochemically erodable workpiece which comprises: a mount for carrying said workpiece; a shaping cathode member mounted at an end of at least one pushrod, said shaping cathode member having a face and a back surface, the cross-sectional area of said cathode member taken through a plane perpendicular to the axis of said pushrod being substantially greater than the same total crosssectional area of all said pushrods; drive means to move said at least one pushrod in a direction generally parallel to the axis of said at least one pushrod to ring the face of said cathode into close proximity with a workpiece carried by said mount to define a work gap between said cathode and workpiece, and to advance the cathode into the workpiece; means, including conduits within said pushrods, for passing a stream of pressurized liquid electrolyte through said work gap, whereby a relative retractive force is exerted between the face of said cathode and the workpiece when pressurized electrolyte is passed through said work gap; cover means to enclose said cathode member and workpiece, and an insulating spacer having a wall engaging said workpiece to define a sealed chamber behind the back surface of said cathode member, said at least one pushrod passing through said cover means in sealingly slidable relationship thereto, said cathode member being movable with respect to said cover means; means for supplying pressurized fluid to said chamber to exert pressure against said cathode back surface for at least partially counteracting said relative retractive force; means responsive to the pressure in said work gap to control the pressure of said fluid supplied to said chamber and to maintain said pressure exerted against said cathode back surface in generally proportional relation to the pressure in said work gap; and means for passing direct electric current between said cathode face and said workpiece in a sense to make the workpiece anodic.

17. The apparatus of claim 16 in which a plurality of electrolyte flow channels lead through said cathode member between said work gap and the conduits in said pushrods.

18. The apparatus of claim 17 in which an electrolyte conduit forms an open path between said chamber and work gap to permit the flow of electrolyte therebetween.

19. The apparatus of claim 18 in which electrolyte passes through said work gap via an electrolyte flow path including at least a portion of said electrolyte conduit and including said electrolyte flow channels which lead through said cathode member between the work gap and the conduits in said at least one pushrod.

! I I Q l Dedication 3,616,433.Ly'nn A. Williams, Winnetka, I11. ELECTROCHEMICAL MA- CHIN IN G APPARATUS HAVING ELECTROLYTE PRES- SURE RESPONSIVE LOAD COMPENSATING MEANS. Patent dated Oct. 26, 1971. Dedication filed Dec. 23, 1971, by the assignee, A'nocut Engineering Oompcm Hereby dedicates to the Public the portion of the term of the patent subsequent to Dec. 24, 1971.

[Oyficz'al Gazette April 25, 1972.] 

2. The apparatus of claim 1 in which the inner wall of said insulating spacer defines a collecting groove that extends around the perimeter of said spacer and communicates with said drain passage that passes through the spacer.
 3. The apparatus of claim 1 in which said insulating spacer has a bottom surface generally complementary to the upper surface of said mount, said bottom surface defining at least one drain groove that extends from the interface between the spacer and workpiece to a zone having a fluid pressure lOwer than that in said sealed chamber.
 4. The apparatus of claim 3 in which the bottom surface of the insulating spacer has a plurality of drain grooves as there defined, said drain grooves being interconnected by a collecting groove in the inner wall of said spacer, and in which said spacer also has a plurality of drain holes therethrough, said drain holes being interconnected by a collecting groove in the inner wall of said spacer, all said drain grooves and drain holes being in communication with the atmosphere.
 5. The apparatus of claim 1 which includes a backup wall surrounding said insulating spacer, said backup wall having at least one drain passage therethrough that connects the drain passage that passes through the insulating spacer with a zone having a fluid pressure lower than that in said sealed chamber.
 6. The apparatus of claim 4 which includes a backup wall surrounding said insulating spacer, said backup wall having a plurality of drain passages therethrough that connect said drain grooves and drain holes in the spacer with the atmosphere.
 7. The apparatus of claim 6 in which said drain passages in the backup wall are spaced differently from said plurality of drain grooves and said plurality of drain holes in the insulating spacer, said drain grooves in the spacer being connected with drain passages through the backup wall by means of a collecting groove defined by the outer surface of the spacer and the inner surface of the backup wall, and said drain holes in the spacer being connected with drain passages through the backup wall by means of a collecting groove defined by the outer surface of the spacer and the inner surface of the backup wall, the drain passages through the backup wall being in communication with the atmosphere.
 8. An apparatus for electrolytically machining an electrically conductive and electrochemically erodable workpiece which comprises: a mount for carrying a workpiece; a shaping cathode member; at least one pushrod having said cathode member mounted at an end thereof, said shaping cathode member having a face and a back surface, the cross-sectional area of said cathode member taken through a plane perpendicular to the axis of said pushrod being substantially greater than the same total cross-sectional area of all said pushrods; drive means to move said at least one pushrod in a direction generally parallel to the axis thereof to bring the face of said cathode into close proximity with a workpiece carried by said mount to define a work gap between said cathode and workpiece, and to advance the cathode into the workpiece; means for passing a stream of pressurized liquid electrolyte through said work gap, whereby a relative retractive force is exerted between the face of said cathode and the workpiece when pressurized electrolyte is passed through said work gap; cover means to enclose said cathode member and workpiece, said cathode member being movable with respect to said cover means; an insulating spacer between said cover means and workpiece and cooperating therewith to define a sealed chamber behind the back surface of said cathode member; means for supplying pressurized fluid to said chamber to exert pressure against said cathode back surface for at least partially counteracting said relative retractive force; means responsive to the pressure in said work gap to control the pressure of said fluid supplied to said chamber and to maintain said pressure exerted against said cathode back surface in generally proportional relation to the pressure in said work gap; and means for passing direct electric current between said cathode face and said workpiece in a sense to make the workpiece anodic.
 9. The apparatus of claim 8 in which a plurality of electrolyte flow channels lead through said cathode member, between said work gap and the exterior of the apparatus, and in which some of said electrolyte flow channels constitute electrolyte inlet channels while some of said electrolyte flow channels constitute electrolyte outlet channels with respect to said work area.
 10. The apparatus of claim 9 in which an electrolyte conduit forms an open path between said chamber and work gap to permit the flow of electrolyte therebetween.
 11. The apparatus of claim 10 in which electrolyte passes through said work gap via an electrolyte flow path including at least a portion of said electrolyte conduit and including said electrolyte flow channels which lead through said cathode member.
 12. The apparatus of claim 11 in which said cathode face is a three-dimensional surface having high areas and low areas, said high areas generally coming into close proximity with a flat workpiece before the low areas as said cathode face and said workpiece are moved together; some of said electrolyte channels leading from said work area through said high areas, and some of said electrolyte channels leading from said work area through said low areas; said apparatus having means for blocking electrolyte flow through said electrolyte flow channels which lead through said low areas until electrolytic machining has proceeded in the workpiece to such a degree that said low areas are in close proximity to said workpiece.
 13. The apparatus of claim 8, including the further improvement of means defining a plurality of outlet flow channels through said cathode member and a plurality of inlet flow channels between said cathode member and said workpiece.
 14. The apparatus of claim 8 in which said cathode member is mounted on a single pushrod member.
 15. The apparatus of claim 8 in which said cathode member is mounted on a plurality of pushrod members.
 16. An apparatus for electrolytically machining an electrically conductive and electrochemically erodable workpiece which comprises: a mount for carrying said workpiece; a shaping cathode member mounted at an end of at least one pushrod, said shaping cathode member having a face and a back surface, the cross-sectional area of said cathode member taken through a plane perpendicular to the axis of said pushrod being substantially greater than the same total cross-sectional area of all said pushrods; drive means to move said at least one pushrod in a direction generally parallel to the axis of said at least one pushrod to bring the face of said cathode into close proximity with a workpiece carried by said mount to define a work gap between said cathode and workpiece, and to advance the cathode into the workpiece; means, including conduits within said pushrods, for passing a stream of pressurized liquid electrolyte through said work gap, whereby a relative retractive force is exerted between the face of said cathode and the workpiece when pressurized electrolyte is passed through said work gap; cover means to enclose said cathode member and workpiece, and an insulating spacer having a wall engaging said workpiece to define a sealed chamber behind the back surface of said cathode member, said at least one pushrod passing through said cover means in sealingly slidable relationship thereto, said cathode member being movable with respect to said cover means; means for supplying pressurized fluid to said chamber to exert pressure against said cathode back surface for at least partially counteracting said relative retractive force; means responsive to the pressure in said work gap to control the pressure of said fluid supplied to said chamber and to maintain said pressure exerted against said cathode back surface in generally proportional relation to the pressure in said work gap; and means for passing direct electric current between said cathode face and said workpiece in a sense to make the workpiece anodic.
 17. The apparatus of claim 16 in which a plurality of electrolyte flow channels lead through said cathode member between said work gap and the conduits in said pushrods.
 18. The apparatus of claim 17 in which an electrolyte conduit forms an open path between said chamber and work gap to permit the flow of electrolyte therebetween.
 19. The apparatus of claim 18 in whiCh electrolyte passes through said work gap via an electrolyte flow path including at least a portion of said electrolyte conduit and including said electrolyte flow channels which lead through said cathode member between the work gap and the conduits in said at least one pushrod. 